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| Mathematical Functions |

## Classes

class | BSpline
class | BSplineBase
class | CatmullRomSpline
class | CoscotFunction
class | Gaussian

## Functions

template<class Iterator>
Iterator | argMax (Iterator first, Iterator last)
template<class Iterator, class UnaryFunctor>
Iterator | argMaxIf (Iterator first, Iterator last, UnaryFunctor condition)
template<class Iterator>
Iterator | argMin (Iterator first, Iterator last)
template<class Iterator, class UnaryFunctor>
Iterator | argMinIf (Iterator first, Iterator last, UnaryFunctor condition)
UInt32 | ceilPower2 (UInt32 x)
double | chi2 (unsigned int degreesOfFreedom, double arg, double accuracy=1e-7)
double | chi2CDF (unsigned int degreesOfFreedom, double arg, double accuracy=1e-7)
template<class T1, class T2>
bool | closeAtTolerance (T1 l, T2 r, typename PromoteTraits< T1, T2 >::Promote epsilon)
double | ellipticIntegralE (double x, double k)
double | ellipticIntegralF (double x, double k)
double | erf (double x)
UInt32 | floorPower2 (UInt32 x)
template<typename IntType>
IntType | gcd (IntType n, IntType m)
double | hypot (double a, double b)
template<typename IntType>
IntType | lcm (IntType n, IntType m)
Int32 | log2i (UInt32 x)
double | noncentralChi2 (unsigned int degreesOfFreedom, double noncentrality, double arg, double accuracy=1e-7)
double | noncentralChi2CDF (unsigned int degreesOfFreedom, double noncentrality, double arg, double accuracy=1e-7)
double | noncentralChi2CDFApprox (unsigned int degreesOfFreedom, double noncentrality, double arg)
template<class T>
NormTraits< T >::NormType | norm (T const &t)
result_type | operator() (argument_type x) const
float | round (float t)
template<class T1, class T2>
T1 | sign (T1 t1, T2 t2)
template<class T>
T | sign (T t)
template<class T>
NumericTraits< T >::Promote | sq (T t)
UInt32 | sqrti (UInt32 v)
Int32 | sqrti (Int32 v)
NormTraits< T >::SquaredNormType | squaredNorm (T const &t)

## Detailed Description

Useful mathematical functions and functors.

## Function Documentation

float vigra::round | ( | float | t | ) |

The rounding function.

Defined for all floating point types. Rounds towards the nearest integer such that `abs(round(t)) == round(abs(t))` for all `t`.

#include <vigra/mathutil.hxx>
Namespace: vigra

UInt32 vigra::ceilPower2 | ( | UInt32 | x | ) |

Round up to the nearest power of 2.

Efficient algorithm for finding the smallest power of 2 which is not smaller than x (function clp2() from Henry Warren: "Hacker's Delight", Addison-Wesley, 2003, see http://www.hackersdelight.org/). If x > 2^31, the function will return 0 because integer arithmetic is defined modulo 2^32.

#include <vigra/mathutil.hxx>
Namespace: vigra

UInt32 vigra::floorPower2 | ( | UInt32 | x | ) |

Round down to the nearest power of 2.

Efficient algorithm for finding the largest power of 2 which is not greater than x (function flp2() from Henry Warren: "Hacker's Delight", Addison-Wesley, 2003, see http://www.hackersdelight.org/).

#include <vigra/mathutil.hxx>
Namespace: vigra

Int32 vigra::log2i | ( | UInt32 | x | ) |

Compute the base-2 logarithm of an integer.

Returns the position of the left-most 1-bit in the given number x, or -1 if x == 0. That is,

            assert(k >= 0 && k < 32 && log2i(1 << k) == k);

The function uses Robert Harley's algorithm to determine the number of leading zeros in x (algorithm nlz10() at http://www.hackersdelight.org/). But note that the functions floorPower2() or ceilPower2() are more efficient and should be preferred when possible.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class T>
NumericTraits<T>::Promote vigra::sq | ( | T | t | ) |

The square function.

`sq(x) = x*x` is needed so often that it makes sense to define it as a function.

#include <vigra/mathutil.hxx>
Namespace: vigra

Int32 vigra::sqrti | ( | Int32 | v | ) |

Signed integer square root.

Useful for fast fixed-point computations.

#include <vigra/mathutil.hxx>
Namespace: vigra

UInt32 vigra::sqrti | ( | UInt32 | v | ) |

Unsigned integer square root.

Useful for fast fixed-point computations.

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::hypot | ( | double | a,
|  | double | b |
| ) |  |  |

Compute the Euclidean distance (length of the hypothenuse of a right-angled triangle).

The hypot() function returns the sqrt(a*a + b*b). It is implemented in a way that minimizes round-off error.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class T>
T vigra::sign | ( | T | t | ) |

The sign function.

Returns 1, 0, or -1 depending on the sign of t.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class T1, class T2>
T1 vigra::sign | ( | T1 | t1,
|  | T2 | t2 |
| ) |  |  |

The binary sign function.

Transfers the sign of t2 to t1.

#include <vigra/mathutil.hxx>
Namespace: vigra

NormTraits<T>::SquaredNormType vigra::squaredNorm | ( | T const & | t | ) |

The squared norm of a numerical object.

For scalar types: equals `vigra::sq(t)`
. For vectorial types: equals `vigra::dot(t, t)`
. For complex types: equals `vigra::sq(t.real()) + vigra::sq(t.imag())`
. For matrix types: results in the squared Frobenius norm (sum of squares of the matrix elements).

template<class T>
NormTraits<T>::NormType vigra::norm | ( | T const & | t | ) |

The norm of a numerical object.

For scalar types: implemented as `abs(t)`
otherwise: implemented as `sqrt(squaredNorm(t))`.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class Iterator>
Iterator vigra::argMin | ( | Iterator | first,
|  | Iterator | last |
| ) |  |  |

Find the minimum element in a sequence.

The function returns the iterator refering to the minimum element.

Required Interface:

            Iterator is a standard forward iterator.

            bool f = *first < NumericTraits<typename std::iterator_traits<Iterator>::value_type>::max();

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class Iterator>
Iterator vigra::argMax | ( | Iterator | first,
|  | Iterator | last |
| ) |  |  |

Find the maximum element in a sequence.

The function returns the iterator refering to the maximum element.

Required Interface:

            Iterator is a standard forward iterator.

            bool f = NumericTraits<typename std::iterator_traits<Iterator>::value_type>::min() < *first;

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class Iterator, class UnaryFunctor>
Iterator vigra::argMinIf | ( | Iterator | first,
|  | Iterator | last,
|  | UnaryFunctor | condition |
| ) |  |  |

Find the minimum element in a sequence conforming to a condition.

The function returns the iterator refering to the minimum element, where only elements conforming to the condition (i.e. where `condition(*iterator)` evaluates to `true`) are considered. If no element conforms to the condition, or the sequence is empty, the end iterator last is returned.

Required Interface:

            Iterator is a standard forward iterator.

            bool c = condition(*first);

            bool f = *first < NumericTraits<typename std::iterator_traits<Iterator>::value_type>::max();

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class Iterator, class UnaryFunctor>
Iterator vigra::argMaxIf | ( | Iterator | first,
|  | Iterator | last,
|  | UnaryFunctor | condition |
| ) |  |  |

Find the maximum element in a sequence conforming to a condition.

The function returns the iterator refering to the maximum element, where only elements conforming to the condition (i.e. where `condition(*iterator)` evaluates to `true`) are considered. If no element conforms to the condition, or the sequence is empty, the end iterator last is returned.

Required Interface:

            Iterator is a standard forward iterator.

            bool c = condition(*first);

            bool f = NumericTraits<typename std::iterator_traits<Iterator>::value_type>::min() < *first;

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::ellipticIntegralF | ( | double | x,
|  | double | k |
| ) |  |  |

The incomplete elliptic integral of the first kind.

Computes

according to the algorithm given in Press et al. "Numerical Recipes".

Note: In some libraries (e.g. Mathematica), the second parameter of the elliptic integral functions must be k^2 rather than k. Check the documentation when results disagree!

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::ellipticIntegralE | ( | double | x,
|  | double | k |
| ) |  |  |

The incomplete elliptic integral of the second kind.

Computes

according to the algorithm given in Press et al. "Numerical Recipes". The complete elliptic integral of the second kind is simply `ellipticIntegralE(M_PI/2, k)`.

Note: In some libraries (e.g. Mathematica), the second parameter of the elliptic integral functions must be k^2 rather than k. Check the documentation when results disagree!

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::erf | ( | double | x | ) |

The error function.

If `erf()` is not provided in the C standard math library (as it should according to the new C99 standard ?), VIGRA implements `erf()` as an approximation of the error function

according to the formula given in Press et al. "Numerical Recipes".

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::chi2 | ( | unsigned int | degreesOfFreedom,
|  | double | arg,
|  | double | accuracy = `1e-7` |
| ) |  |  |

Chi square distribution.

Computes the density of a chi square distribution with degreesOfFreedom and tolerance accuracy at the given argument arg by calling `noncentralChi2(degreesOfFreedom, 0.0, arg, accuracy)`.

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::chi2CDF | ( | unsigned int | degreesOfFreedom,
|  | double | arg,
|  | double | accuracy = `1e-7` |
| ) |  |  |

Cumulative chi square distribution.

Computes the cumulative density of a chi square distribution with degreesOfFreedom and tolerance accuracy at the given argument arg, i.e. the probability that a random number drawn from the distribution is below arg by calling `noncentralChi2CDF(degreesOfFreedom, 0.0, arg, accuracy)`.

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::noncentralChi2 | ( | unsigned int | degreesOfFreedom,
|  | double | noncentrality,
|  | double | arg,
|  | double | accuracy = `1e-7` |
| ) |  |  |

Non-central chi square distribution.

Computes the density of a non-central chi square distribution with degreesOfFreedom, noncentrality parameter noncentrality and tolerance accuracy at the given argument arg. It uses Algorithm AS 231 from Appl. Statist. (1987) Vol.36, No.3 (code ported from http://lib.stat.cmu.edu/apstat/231). The algorithm has linear complexity in the number of degrees of freedom.

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::noncentralChi2CDF | ( | unsigned int | degreesOfFreedom,
|  | double | noncentrality,
|  | double | arg,
|  | double | accuracy = `1e-7` |
| ) |  |  |

Cumulative non-central chi square distribution.

Computes the cumulative density of a chi square distribution with degreesOfFreedom, noncentrality parameter noncentrality and tolerance accuracy at the given argument arg, i.e. the probability that a random number drawn from the distribution is below arg It uses Algorithm AS 231 from Appl. Statist. (1987) Vol.36, No.3 (code ported from http://lib.stat.cmu.edu/apstat/231). The algorithm has linear complexity in the number of degrees of freedom (see noncentralChi2CDFApprox() for a constant-time algorithm).

#include <vigra/mathutil.hxx>
Namespace: vigra

double vigra::noncentralChi2CDFApprox | ( | unsigned int | degreesOfFreedom,
|  | double | noncentrality,
|  | double | arg |
| ) |  |  |

Cumulative non-central chi square distribution (approximate).

Computes approximate values of the cumulative density of a chi square distribution with degreesOfFreedom, and noncentrality parameter noncentrality at the given argument arg, i.e. the probability that a random number drawn from the distribution is below arg It uses the approximate transform into a normal distribution due to Wilson and Hilferty (see Abramovitz, Stegun: "Handbook of Mathematical Functions", formula 26.3.32). The algorithm's running time is independent of the inputs, i.e. is should be used when noncentralChi2CDF() is too slow, and approximate values are sufficient. The accuracy is only about 0.1 for few degrees of freedom, but reaches about 0.001 above dof = 5.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<class T1, class T2>
bool vigra::closeAtTolerance | ( | T1 | l,
|  | T2 | r,
|  | typename PromoteTraits< T1, T2 >::Promote | epsilon |
| ) |  |  |

Tolerance based floating-point comparison.

Check whether two floating point numbers are equal within the given tolerance. This is useful because floating point numbers that should be equal in theory are rarely exactly equal in practice. If the tolerance epsilon is not given, twice the machine epsilon is used.

#include <vigra/mathutil.hxx>
Namespace: vigra

template<typename IntType>
IntType vigra::gcd | ( | IntType | n,
|  | IntType | m |
| ) |  |  |

Calculate the greatest common divisor.

This function works for arbitrary integer types, including user-defined (e.g. infinite precision) ones.

#include <vigra/rational.hxx>
Namespace: vigra

template<typename IntType>
IntType vigra::lcm | ( | IntType | n,
|  | IntType | m |
| ) |  |  |

Calculate the lowest common multiple.

This function works for arbitrary integer types, including user-defined (e.g. infinite precision) ones.

#include <vigra/rational.hxx>
Namespace: vigra

CatmullRomSpline< T >::result_type operator() | ( | argument_type | x | ) | const`[inherited]`

function (functor) call

© Ullrich Köthe (ullrich.koethe@iwr.uni-heidelberg.de) Heidelberg Collaboratory for Image Processing, University of Heidelberg, Germany | html generated using doxygen and Python VIGRA 1.6.0 (13 Aug 2008)